/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.analysis;

import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.util.Version;

import java.io.IOException;

/**
 * A TokenFilter which filters out Tokens at the same position and Term text as
 * the previous token in the stream.
 */
public final class RemoveDuplicatesTokenFilter extends TokenFilter {

	private final CharTermAttribute termAttribute = addAttribute(CharTermAttribute.class);
	private final PositionIncrementAttribute posIncAttribute = addAttribute(PositionIncrementAttribute.class);

	// use a fixed version, as we don't care about case sensitivity.
	private final CharArraySet previous = new CharArraySet(Version.LUCENE_31,
			8, false);

	/**
	 * Creates a new RemoveDuplicatesTokenFilter
	 * 
	 * @param in
	 *            TokenStream that will be filtered
	 */
	public RemoveDuplicatesTokenFilter(TokenStream in) {
		super(in);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public boolean incrementToken() throws IOException {
		while (input.incrementToken()) {
			final char term[] = termAttribute.buffer();
			final int length = termAttribute.length();
			final int posIncrement = posIncAttribute.getPositionIncrement();

			if (posIncrement > 0) {
				previous.clear();
			}

			boolean duplicate = (posIncrement == 0 && previous.contains(term,
					0, length));

			// clone the term, and add to the set of seen terms.
			char saved[] = new char[length];
			System.arraycopy(term, 0, saved, 0, length);
			previous.add(saved);

			if (!duplicate) {
				return true;
			}
		}
		return false;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void reset() throws IOException {
		super.reset();
		previous.clear();
	}
}
